36 BULLETIN 842, U. S. DEPARTMENT OF AGRICULTURE. 
retain their green color longer than normal spikes. They are reduced 
in length and have their glumes spread out at greater angles than 
uninfected spikes. In place of normal kernels the glumes contain 
dark, hard galls, which are shorter and frequently thicker than 
wheat grains and which may be seen sometimes partly exposed in 
diseased spikes. Because of a general similarity, these galls often 
have been mistaken for the seed of cockle (Agrostemma githago), a 
weed which occurs commonly in wheat fields, for kernels affected by 
stinking smut due to Tilletia tritici, and for bin-burnt wheat caused 
by overheating the stored grain. 
The disease is caused by a minute nematode, Tylenchus tritici 
(Steinbuch) Bastian, the larval stage of which in great numbers 
may be seen with the unaided eye when a gall is teased apart in 
water. These larvae in mass appear milky white in color. Indi- 
vidually they are threadlike animals, nearly 1 millimeter in length 
and capable of an eellike movement. Under favorable conditions 
of moisture and temperature they escape from the galls which have 
fallen to the ground or have been sown along with wheat seed, and 
by their own movement reach the young seedlings. They finally be- 
come located between the leaf sheaths near the terminal stem bud 
and in this region are passively elevated to the inflorescence. Occa- 
sionally they penetrate the leaves and induce small swellings, but 
usually they enter only the embryonic flowers, which develop into 
galls instead of kernels. In these places the larvae, after several 
metamorphoses, develop into about equal numbers of male and 
female adults, the former about 2 mm. in length and the latter 
from 3 to 5 mm. long. Each female may lay more than 2,000 eggs. 
Measuring approximately 37 p* ^ T ide by 85 pi long, these eggs are 
elongate, ellipsoidal, granular bodies, which in a short time after ovi- 
position develop into larvae and in this manner complete the life his- 
tory of the organism. At the maturity of the plant the larvae within 
the gall become inactive, dried, and motionless, in which lethargic 
condition they can remain alive for many years. 
The larvae inclosed in galls were killed by an immersion in water 
at temperatures of 50°, 52°, 54°, and 56° C. for 30, 20, 10, and 5 
minutes, respectively, provided the galls were thoroughly moistened 
before the treatment. Much longer immersions at the same tem- 
peratures are necessary to kill them if the galls are dry when 
treated. Free from the protective gall, the larvae succumb to tem- 
peratures of 50° and 52° C. in 15 and 10 minutes, respectively ; that 
is, in half the time required to kill them within the galls. Larvae 
either inside or outside the protective gall are highly resistant to 
the toxic action of formaldehyde, mercuric chlorid, copper sulphate, 
and sulphuric acid. They live after long submersion in concentra- 
